Tight Oil Potential in Japan

Abstract

The Onnagawa Shale is bio-siliceous, Monterey-like and the main source rock in Japan, particularly in Akita basin, with fairly high potential. It is 500m thick in average and has TOC of 2％ in average, up to 5％ in part, and HI of 500 mg/gC typically. The Onnagawa is under review in the light of Shale oil/gas, comparing the Monterey shale. As the rst step, we have reviewed the Yuihara-Ayukawa eld, where the largest commercial oil & gas production from the Onnagawa Shale is ongoing. In the eld, various reservoirs, including Dolerite, Tuff and quartzose porcelanite probably fractured, seem to have a common gas-oil contact. In other words, they constitute one pressure system. The maturity of the hydrocarbon in this system is much higher than that of source rocks close to the reservoirs, which indicates normal migration process. We also have sub-commercial production or intense oil show from relatively tight reservoirs that is typically alternation of porcelanite and tuff. The maturity of the oil, however, is lower than that of commercial oils and close to that of early-matured source rocks around. In summary, we have two different hydrocarbon accumulations in one led. One is productive, mature and probably migrated, and another is sub-commercial or non-productive so far, less matured and indigenous. In addition, we have other similar examples in the Akita basin and we think this less-matured oil group as a part of basin-wide shale oil system, where our eld is located in the transition zone just above oil generation window. We expect a potential with an order of 100 million bbl in this basin including the kitchen. Now the rst pilot test is being planned to apply horizontal drilling and massive stimulation treatment to "shale oil or tight oil" in this basin.

Acid Stimulation of Onnagawa Tight Oil Formation in Ayukawa Field, Japan

“…This tight reservoir is interpreted as part of the tight oil system of a continuous accumulation including the kitchen. The tight oil potential around this field is expected approximately 100 million bbl (Yokoi et al 2013). …”

Damage Evolution of Onnagawa Shale by Postmortem Thresholding of X‐Ray Computed Tomography

“…Shale samples used in the current study are from the Miocene Onnagawa formation (Acocella et al., 2008; Figure 1) collected from an outcrop of Akita Gojome area in northeastern Japan (39.9146767, 140.2466342). They are clay poor biosiliceous shales (Kamitsuji et al., 2013; Yokoi et al., 2012) with 68 vol% quartz, 27 vol% feldspar, 3 vol% kaolinite, 1 vol% chlorite, 0.5 vol% pyrite, and 0.5 vol% other minerals (see Figure S1 for XRD results). The He pycnometry showed that these samples have a very high connected porosity of about 34.5% similar to the results of Kamitsuji et al.…”

The hydrocarbon potential of the Miocene siliceous formations in Tsugaru Basin, northern Japan, based on the geochemical analyses

“…Another possibility that should be considered is the effect of igneous intrusions on thermal maturity. Yokoi et al (2013) demonstrated that in the Ayukawa oil & gas field, the Onnagawa Formation is mature even at depths shallower The stratigraphic columns were compiled using data from this study, the Japanese National Gas Association (1992) , and the Japanese Association for Petroleum Technology (1993) . Iwasa, 1962;Ujiie, 1995) .…”

“…1) . A notable example of source rock for conventional and unconventional oil and gas exploration is the Onnagawa Formation in Akita Prefecture (Aoyagi and Omokawa, 1992;Japan National Gas Association, 1992; Japan Association for Petroleum Technology, 1993;Yokoi et al, 2013;Kumada et al, 2018) . Previous studies on the siliceous mudstones in the western Aomori Prefecture revealed that the Odoji Formation, cor relatable with the Onnagawa Formation, is a potential source rock for hydrocarbons (Aoyagi and Omokawa, 1992;Ujiie, 1995;Martizzi et al, 2020) .…”